Debris sensor for cleaning apparatus

ABSTRACT

A piezoelectric debris sensor and associated signal processor responsive to debris strikes enable an autonomous or non-autonomous cleaning device to detect the presence of debris and in response, to select a behavioral mode, operational condition or pattern of movement, such as spot coverage or the like. Multiple sensor channels (e.g., left and right) can be used to enable the detection or generation of differential left/right debris signals and thereby, enable an autonomous device to steer in the direction of debris.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 USC 120) of U.S. application Ser. No. 13/350,447, filed Jan.13, 2012, which is a continuation of U.S. application Ser. No.12/750,506, filed Mar. 30, 2010 (issued on Jan. 31, 2012 as U.S. Pat.No. 8,107,318), which is a continuation of U.S. application Ser. No.12/115,229, filed May 5, 2008 (issued on Mar. 30, 2010 as U.S. Pat. No.7,688,676), which is a continuation of, and claims priority under 35U.S.C. .sctn.120 from, U.S. patent application Ser. No. 11/085,832,filed on Mar. 21, 2005 (issued on May 6, 2008 as U.S. Pat. No.7,369,460), which is a continuation-in-part of, and claims priority to,U.S. patent application Ser. No. 09/921,181, filed on Aug. 2, 2001(issued on Mar. 22, 2005 as U.S. Pat. No. 6,870,792), which claimspriority under 35 U.S.C. .sctn.119(e) to U.S. Provisional ApplicationNo. 60/222,542, filed on Aug. 3, 2000. The disclosures of these priorapplications are considered part of the disclosure of this applicationand are hereby incorporated by reference in their entireties.

U.S. patent application Ser. No. 09/826,209, filed Apr. 4, 2001, andU.S. Provisional Application No. 60/194,922, filed Apr. 4, 2000 are alsoincorporated by reference into this application as if set forth hereinin full, although no priority claim is made to these two applications

FIELD OF INVENTION

The present invention relates generally to cleaning apparatus, and, moreparticularly, to a debris sensor for sensing instantaneous strikes bydebris in a cleaning path of a cleaning apparatus and for enablingcontrol of an operational mode of the cleaning apparatus. The term“debris” is used herein to collectively denote dirt, dust and/or otherparticulates or objects that might be collected by a vacuum cleaner orother cleaning apparatus, whether autonomous or non-autonomous.

BACKGROUND

Debris sensors, including some suitable for cleaning apparatus, areknown in the art. Debris sensors can be useful in autonomous cleaningdevices like those disclosed in the above-referenced patentapplications, and can also be useful in non-autonomous cleaning devices,whether to indicate to the user that a particularly dirty area is beingentered, to increase a power setting in response to detection of debris,or to modify some other operational setting.

Examples of debris sensors are disclosed in the following:TABLE-US-00001 De Brey U.S. Pat. No. 3,674,316 De Brey U.S. Pat. No.3,989,311 De Brey U.S. Pat. No. 4,175,892 Kurz U.S. Pat. No. 4,601,082Westergren U.S. Pat. No. 4,733,430 Martin U.S. Pat. No. 4,733,431Harkonen U.S. Pat. No. 4,829,626 Takashima U.S. Pat. No. 5,105,502Takashima U.S. Pat. No. 5,136,750 Kawakami U.S. Pat. No. 5,163,202 YangU.S. Pat. No. 5,319,827 Kim U.S. Pat. No. 5,440,216 Gordon U.S. Pat. No.5,608,944 Imamura U.S. Pat. No. 5,815,884 Imamura U.S. Pat. No.6,023,814 Kasper U.S. Pat. No. 6,446,302 Gordon U.S. Pat. No. 6,571,422

Among the examples disclosed therein, many such debris sensors areoptical in nature, using a light emitter and detector. In typicaldesigns used in, e.g., a vacuum cleaner, the light transmitter and thelight receiver of the optical sensor are positioned such that they areexposed into the suction passage or cleaning pathway through which dustflows. During usage of the vacuum cleaner, therefore, dust particlestend to adhere to the exposed surfaces of the light transmitter and thelight receiver, through which light is emitted and detected, eventuallydegrading the performance of the optical sensor.

Accordingly, it would be desirable to provide a debris sensor that isnot subject to degradation by accretion of debris.

In addition, debris sensors typical of the prior art are sensitive to alevel of built-up debris in a reservoir or cleaning pathway, but notparticularly sensitive to instantaneous debris strikes or encounters.

It would therefore be desirable to provide a debris sensor that iscapable of instantaneously sensing and responding to debris strikes, andwhich is immediately responsive to debris on a floor or other surface tobe cleaned, with reduced sensitivity to variations in airflow,instantaneous power, or other operational conditions of the cleaningdevice.

It would be also be useful to provide an autonomous cleaning devicehaving operational modes, patterns of movement or behaviors responsiveto detected debris, for example, by steering the device toward “dirtier”areas based on signals generated by a debris sensor.

In addition, it would be desirable to provide a debris sensor that couldbe used to control, select or vary operational modes of either anautonomous or non-autonomous cleaning apparatus.

SUMMARY

The present invention provides a debris sensor, and apparatus utilizingsuch a debris sensor, wherein the sensor is instantaneously responsiveto debris strikes, and can be used to control, select or vary theoperational mode of an autonomous or non-autonomous cleaning apparatuscontaining such a sensor.

One aspect of the invention is an autonomous cleaning apparatusincluding a drive system operable to enable movement of the cleaningapparatus; a controller in communication with the drive system, thecontroller including a processor operable to control the drive system toprovide at least one pattern of movement of the cleaning apparatus; anda debris sensor for generating a debris signal indicating that thecleaning apparatus has encountered debris; wherein the processor isresponsive to the debris signal to select an operative mode from amongpredetermined operative modes of the cleaning apparatus.

The selection of operative mode could include selecting a pattern ofmovement of the cleaning apparatus.

The pattern of movement can include spot coverage of an area containingdebris, or steering the cleaning apparatus toward an area containingdebris. The debris sensor could include spaced-apart first and seconddebris sensing elements respectively operable to generate first andsecond debris signals; and the processor can be responsive to therespective first and second debris signals to select a pattern ofmovement, such as steering toward a side (e.g., left or right side) withmore debris.

The debris sensor can include a piezoelectric sensor element locatedproximate to a cleaning pathway of the cleaning apparatus and responsiveto a debris strike to generate a signal indicative of such strike.

The debris sensor of the invention can also be incorporated into anon-autonomous cleaning apparatus. This aspect of the invention caninclude a piezoelectric sensor located proximate to a cleaning pathwayand responsive to a debris strike to generate a debris signal indicativeof such strike; and a processor responsive to the debris signal tochange an operative mode of the cleaning apparatus. The change inoperative mode could include illuminating a user-perceptible indicatorlight, changing a power setting (e.g., higher power setting when moredebris is encountered), or slowing or reducing a movement speed of theapparatus.

A further aspect of the invention is a debris sensor, including apiezoelectric element located proximate to or within a cleaning pathwayof the cleaning apparatus and responsive to a debris strike to generatea first signal indicative of such strike; and a processor operable toprocess the first signal to generate a second signal representative of acharacteristic of debris being encountered by the cleaning apparatus.That characteristic could be, for example, a quantity or volumetricparameter of the debris, or a vector from a present location of thecleaning apparatus to an area containing debris.

Another aspect of the invention takes advantage of the motion of anautonomous cleaning device across a floor or other surface, processingthe debris signal in conjunction with knowledge of the cleaning device'smovement to calculate a debris gradient. The debris gradient isrepresentative of changes in debris strikes count as the autonomouscleaning apparatus moves along a surface. By examining the sign of thegradient (positive or negative, associated with increasing or decreasingdebris), an autonomous cleaning device controller can continuouslyadjust the path or pattern of movement of the device to clean a debrisfield most effectively.

These and other aspects, features and advantages of the invention willbecome more apparent from the following description, in conjunction withthe accompanying drawings, in which embodiments of the invention areshown and described by way of illustrative example.

DESCRIPTION OF DRAWINGS

A more complete understanding of the present invention and the attendantfeatures and advantages thereof may be had by reference to the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a top-view schematic of an exemplary autonomous cleaningdevice in which the debris sensor of the invention can be employed.

FIG. 2 is a block diagram of exemplary hardware elements of the roboticdevice of FIG. 1, including a debris sensor subsystem of the invention.

FIG. 3 is a side view of the robotic device of FIG. 1, showing a debrissensor according to the invention situated in a cleaning or vacuumpathway, where it will be struck by debris upswept by the main cleaningbrush element.

FIG. 4 is an exploded diagram of a piezoelectric debris sensor inaccordance with the invention.

FIG. 5 is a schematic diagram of a debris sensor signal processingarchitecture according to the present invention.

FIG. 6 is a schematic diagram of signal processing circuitry for thedebris sensor architecture of FIG. 5.

FIG. 6A is a schematic diagram of a first portion of the signalprocessing circuitry.

FIG. 6B is a schematic diagram of a second portion of the signalprocessing circuitry.

FIG. 6C is a schematic diagram of a third portion of the signalprocessing circuitry.

FIG. 7 is a schematic diagram showing the debris sensor in anon-autonomous cleaning apparatus.

FIG. 8 is a flowchart of a method according to one practice of theinvention.

DETAILED DESCRIPTION

While the debris sensor of the present invention can be incorporatedinto a wide range of autonomous cleaning devices (and indeed, intonon-autonomous cleaning devices as shown by way of example in FIG. 7),it will first be described in the context of an exemplary autonomouscleaning device shown in FIGS. 1-3. Further details of the structure,function and behavioral modes of such an autonomous cleaning device areset forth in the patent applications cited above in the Cross-Referencesection, each of which is incorporated herein by reference. Accordingly,the following detailed description is organized into the followingsections:

I. Exemplary Autonomous Cleaning Device

II. Behavioral Modes of an Autonomous Cleaning Device

III. Debris Sensor Structure

IV. Signal Processing

V. Conclusions

I. Autonomous Cleaning Device

Referring now to the drawings wherein like reference numerals identifycorresponding or similar elements throughout the several views, FIG. 1is a top-view schematic of an exemplary autonomous cleaning device 100in which a debris sensor according to the present invention may beincorporated. FIG. 2 is a block diagram of the hardware of the robotdevice 100 of FIG. 1.

Examples of hardware and behavioral modes (coverage behaviors orpatterns of movement for cleaning operations; escape behaviors fortransitory movement patterns; and safety behaviors for emergencyconditions) of an autonomous cleaning device 100 marketed by the iRobotCorporation of Burlington, Mass. under the ROOMBA trademark, will nextbe described to provide a more complete understanding of how the debrissensing system of the present invention may be employed. However, theinvention can also be employed in non-autonomous cleaning devices, andan example is described below in connection with FIG. 7.

In the following description, the terms “forward” and “fore” are used torefer to the primary direction of motion (forward) of the robotic device(see arrow identified by reference character “FM” in FIG. 1). Thefore/aft axis FA.sub.X of the robotic device 100 coincides with themedial diameter of the robotic device 100 that divides the roboticdevice 100 into generally symmetrical right and left halves, which aredefined as the dominant and non-dominant sides, respectively.

An example of such a robotic cleaning device 100 has a generallydisk-like housing infrastructure that includes a chassis 102 and anouter shell 104 secured to the chassis 102 that define a structuralenvelope of minimal height (to facilitate movement under furniture). Thehardware comprising the robotic device 100 can be generally categorizedas the functional elements of a power system, a motive power system(also referred to herein as a “drive system”), a sensor system, acontrol module, a side brush assembly, or a self-adjusting cleaning headsystem, respectively, all of which are integrated in combination withthe housing infrastructure. In addition to such categorized hardware,the robotic device 100 further includes a forward bumper 106 having agenerally arcuate configuration and a nose-wheel assembly 108.

The forward bumper 106 (illustrated as a single component;alternatively, a two-segment component) is integrated in movablecombination with the chassis 102 (by means of displaceable supportmembers pairs) to extend outwardly therefrom. Whenever the roboticdevice 100 impacts an obstacle (e.g., wall, furniture) during movementthereof, the bumper 106 is displaced (compressed) towards the chassis102 and returns to its extended (operating) position when contact withthe obstacle is terminated.

The nose-wheel assembly 108 is mounted in biased combination with thechassis 102 so that the nose-wheel subassembly 108 is in a retractedposition (due to the weight of the robotic device 100) during cleaningoperations wherein it rotates freely over the surface being cleaned.When the nose-wheel subassembly 108 encounters a drop-off duringoperation (e.g., descending stairs, split-level floors), the nose-wheelassembly 108 is biased to an extended position.

The hardware of the power system, which provides the energy to power theelectrically-operated hardware of the robotic device 100, comprises arechargeable battery pack 110 (and associated conduction lines, notshown) that is integrated in combination with the chassis 102.

As shown in FIG. 1, the motive power system provides the means thatpropels the robotic device 100 and operates the cleaning mechanisms,e.g., side brush assembly and the self-adjusting cleaning head system,during movement of the robotic device 100. The motive power systemcomprises left and right main drive wheel assemblies 112L, 112R, theirassociated independent electric motors 114L, 114R, and electric motors116, 118 for operation of the side brush assembly and the self-adjustingcleaning head subsystem, respectively.

The electric motors 114L, 114R are mechanically coupled to the maindrive wheel assemblies 112L, 112R, respectively, and independentlyoperated by control signals generated by the control module as aresponse to the implementation of a behavioral mode, or, as discussed ingreater detail below, in response to debris signals generated by leftand right debris sensors 125L, 125R shown in FIG. 1.

Independent operation of the electric motors 114L, 114R allows the mainwheel assemblies 112L, 112R to be: (1) rotated at the same speed in thesame direction to propel the robotic device 100 in a straight line,forward or aft; (2) differentially rotated (including the conditionwherein one wheel assembly is not rotated) to effect a variety of rightand/or left turning patterns (over a spectrum of sharp to shallow turns)for the robotic device 100; and (3) rotated at the same speed inopposite directions to cause the robotic device 100 to turn in place,i.e., “spin on a dime”, to provide an extensive repertoire of movementcapability for the robotic device 100.

As shown in FIG. 1, the sensor system comprises a variety of differentsensor units that are operative to generate signals that control thebehavioral mode operations of the robotic device 100. The describedrobotic device 100 includes obstacle detection units 120, cliffdetection units 122, wheel drop sensors 124, an obstacle-following unit126, a virtual wall omnidirectional detector 128, stall-sensor units130, main wheel encoder units 132, and, in accordance with the presentinvention, left and right debris sensors 125L and 125R described ingreater detail below.

In the illustrated embodiment, the obstacle (“bump”) detection units 120can be IR break beam sensors mounted in combination with thedisplaceable support member pairs of the forward bumper 106. Thesedetection units 120 are operative to generate one or more signalsindicating relative displacement between one or more support memberpairs whenever the robotic device 100 impacts an obstacle such that theforward bumper 106 is compressed. These signals are processed by thecontrol module to determine an approximate point of contact with theobstacle relative to the fore-aft axis FAX of the robotic device 100(and the behavioral mode(s) to be implemented).

The cliff detection units 122 are mounted in combination with theforward bumper 106. Each cliff detection unit 122 comprises an IRemitter-detector pair configured and operative to establish a focalpoint such that radiation emitted downwardly by the emitter is reflectedfrom the surface being traversed and detected by the detector. Ifreflected radiation is not detected by the detector, i.e., a drop-off isencountered, the cliff detection unit 122 transmits a signal to thecontrol module (which causes one or more behavioral modes to beimplemented).

wheel drop sensor 124 such as a contact switch is integrated incombination with each of the main drive wheel assemblies 112L, 112R andthe nose wheel assembly 108 and is operative to generate a signalwhenever any of the wheel assemblies is in an extended position, i.e.,not in contact with the surface being traversed, (which causes thecontrol module to implement one ore more behavioral modes).

The obstacle-following unit 126 for the described embodiment is an IRemitter-detector pair mounted on the ‘dominant’ side (right hand side ofFIG. 1) of the robotic device 100. The emitter-detector pair is similarin configuration to the cliff detection units 112, but is positioned sothat the emitter emits radiation laterally from the dominant side of therobotic device 100. The unit 126 is operative to transmit a signal tothe control module whenever an obstacle is detected as a result ofradiation reflected from the obstacle and detected by the detector. Thecontrol module, in response to this signal, causes one or morebehavioral modes to be implemented.

A virtual wall detection system for use in conjunction with thedescribed embodiment of the robotic device 100 comprises anomnidirectional detector 128 mounted atop the outer shell 104 and astand-alone transmitting unit (not shown) that transmits anaxially-directed confinement beam. The stand-alone transmitting unit ispositioned so that the emitted confinement beam blocks an accessway to adefined working area, thereby restricting the robotic device 100 tooperations within the defined working area (e.g., in a doorway toconfine the robotic device 100 within a specific room to be cleaned).Upon detection of the confinement beam, the omnidirectional detector 128transmits a signal to the control module (which causes one or morebehavioral modes to be implemented to move the robotic device 100 awayfrom the confinement beam generated by the stand-alone transmittingunit).

A stall sensor unit 130 is integrated in combination with each electricmotor 114L, 114R, 116, 118 and operative to transmit a signal to thecontrol module when a change in current is detected in the associatedelectric motor (which is indicative of a dysfunctional condition in thecorresponding driven hardware). The control module is operative inresponse to such a signal to implement one or more behavioral modes.

An IR encoder unit 132 (see FIG. 2) is integrated in combination witheach main wheel assembly 112L, 112R and operative to detect the rotationof the corresponding wheel and transmit signals corresponding theretothe control module (wheel rotation can be used to provide an estimate ofdistance traveled for the robotic device 100).

Control Module:

Referring now to FIG. 2, the control module comprises themicroprocessing unit 135 that includes I/O ports connected to thesensors and controllable hardware of the robotic device 100, amicrocontroller (such as a Motorola MC9512E128CPV 16-bit controller),and ROM and RAM memory. The I/O ports function as the interface betweenthe microcontroller and the sensor units (including left and rightdebris sensors 125 discussed in greater detail below) and controllablehardware, transferring signals generated by the sensor units to themicrocontroller and transferring control (instruction) signals generatedby the microcontroller to the controllable hardware to implement aspecific behavioral mode.

The microcontroller is operative to execute instruction sets forprocessing sensor signals, implementing specific behavioral modes basedupon such processed signals, and generating control (instruction)signals for the controllable hardware based upon implemented behavioralmodes for the robotic device 100. The cleaning coverage and controlprograms for the robotic device 100 are stored in the ROM of themicroprocessing unit 135, which includes the behavioral modes, sensorprocessing algorithms, control signal generation algorithms and aprioritization algorithm for determining which behavioral mode or modesare to be given control of the robotic device 100. The RAM of themicroprocessing unit 135 is used to store the active state of therobotic device 100, including the ID of the behavioral mode(s) underwhich the robotic device 100 is currently being operated and thehardware commands associated therewith.

Referring again to FIG. 1, there is shown a brush assembly 140,configured and operative to entrain particulates outside the peripheryof the housing infrastructure and to direct such particulates towardsthe self-adjusting cleaning head system. The side brush assembly 140provides the robotic device 100 with the capability of cleaning surfacesadjacent to base-boards when the robotic device is operated in anObstacle-Following behavioral mode. As shown in FIG. 1, the side brushassembly 140 is preferably mounted in combination with the chassis 102in the forward quadrant on the dominant side of the robotic device 100.

The self-adjusting cleaning head system 145 for the described roboticdevice 100 comprises a dual-stage brush assembly and a vacuum assembly,each of which is independently powered by an electric motor (referencenumeral 118 in FIG. 1 actually identifies two independent electricmotors—one for the brush assembly and one for the vacuum assembly). Thecleaning capability of the robotic device 100 is commonly characterizedin terms of the width of the cleaning head system 145 (see referencecharacter W in FIG. 1).

Referring now to FIG. 3, in one embodiment of a robotic cleaning device,the cleaning brush assembly comprises asymmetric, counter-rotatingflapper and main brush elements 92 and 94, respectively, that arepositioned forward of the vacuum assembly inlet 84, and operative todirect particulate debris 127 into a removable dust cartridge 86. Asshown in FIG. 3, the autonomous cleaning apparatus can also include leftand right debris sensor elements 125PS, which can be piezoelectricsensor elements, as described in detail below. The piezoelectric debrissensor elements 125PS can be situated in a cleaning pathway of thecleaning device, mounted, for example, in the roof of the cleaning head,so that when struck by particles 127 swept up by the brush elementsand/or pulled up by vacuum, the debris sensor elements 125PS generateelectrical pulses representative of debris impacts and thus, of thepresence of debris in an area in which the autonomous cleaning device isoperating.

More particularly, in the arrangement shown in FIG. 3, the sensorelements 125PS are located substantially at an axis AX along which mainand flapper brushes 94, 92 meet, so that particles strike the sensorelements 125PS with maximum force.

As shown in FIG. 1, and described in greater detail below, the roboticcleaning device can be fitted with left and right side piezoelectricdebris sensors, to generate separate left and right side debris signalsthat can be processed to signal the robotic device to turn in thedirection of a “dirty” area.

The operation of the piezoelectric debris sensors, as well as signalprocessing and selection of behavioral modes based on the debris signalsthey generate, will be discussed below following a brief discussion ofgeneral aspects of behavioral modes for the cleaning device.

II. Behavioral Modes

The robotic device 100 can employ a variety of behavioral modes toeffectively clean a defined working area where behavioral modes arelayers of control systems that can be operated in parallel. Themicroprocessor unit 135 is operative to execute a prioritizedarbitration scheme to identify and implement one or more dominantbehavioral modes for any given scenario based upon inputs from thesensor system.

The behavioral modes for the described robotic device 100 can becharacterized as: (1) coverage behavioral modes; (2) escape behavioralmodes; and (3) safety behavioral modes. Coverage behavioral modes areprimarily designed to allow the robotic device 100 to perform itscleaning operations in an efficient and effective manner and the escapeand safety behavioral modes are priority behavioral modes implementedwhen a signal from the sensor system indicates that normal operation ofthe robotic device 100 is impaired, e.g., obstacle encountered, or islikely to be impaired, e.g., drop-off detected.

Representative and illustrative coverage behavioral (cleaning) modes forthe robotic device 100 include: (1) a Spot Coverage pattern; (2) anObstacle-Following (or Edge-Cleaning) Coverage pattern, and (3) a RoomCoverage pattern. The Spot Coverage pattern causes the robotic device100 to clean a limited area within the defined working area, e.g., ahigh-traffic area. In a preferred embodiment the Spot Coverage patternis implemented by means of a spiral algorithm (but other types ofself-bounded area algorithms, e.g., polygonal, can be used). The spiralalgorithm, which causes outward spiraling (preferred) or inwardspiraling movement of the robotic device 100, is implemented by controlsignals from the microprocessing unit 135 to the main wheel assemblies112L, 112R to change the turn radius/radii thereof as a function of time(thereby increasing/decreasing the spiral movement pattern of therobotic device 100).

The robotic device 100 is operated in the Spot Coverage pattern for apredetermined or random period of time, for a predetermined or randomdistance (e.g., a maximum spiral distance) and/or until the occurrenceof a specified event, e.g., activation of one or more of the obstacledetection units 120 (collectively a transition condition). Once atransition condition occurs, the robotic device 100 can implement ortransition to a different behavioral mode, e.g., a Straight Linebehavioral mode (in a preferred embodiment of the robotic device 100,the Straight Line behavioral mode is a low priority, default behaviorthat propels the robot in an approximately straight line at a presetvelocity of approximately 0.306 m/s) or a Bounce behavioral mode incombination with a Straight Line behavioral mode.

If the transition condition is the result of the robotic device 100encountering an obstacle, the robotic device 100 can take other actionsin lieu of transitioning to a different behavioral mode. The roboticdevice 100 can momentarily implement a behavioral mode to avoid orescape the obstacle and resume operation under control of the spiralalgorithm (i.e., continue spiraling in the same direction).Alternatively, the robotic device 100 can momentarily implement abehavioral mode to avoid or escape the obstacle and resume operationunder control of the spiral algorithm (but in the oppositedirection-reflective spiraling).

The Obstacle-Following Coverage pattern causes the robotic device 100 toclean the perimeter of the defined working area, e.g., a room bounded bywalls, and/or the perimeter of an obstacle (e.g., furniture) within thedefined working area. Preferably the robotic device 100 of FIG. 1utilizes obstacle-following unit 126 (see FIG. 1) to continuouslymaintain its position with respect to an obstacle, e.g., wall,furniture, so that the motion of the robotic device 100 causes it totravel adjacent to and concomitantly clean along the perimeter of theobstacle. Different embodiments of the obstacle-following unit 126 canbe used to implement the Obstacle-Following behavioral pattern.

In a first embodiment, the obstacle-following unit 126 is operated todetect the presence or absence of the obstacle. In an alternativeembodiment, the obstacle-following unit 126 is operated to detect anobstacle and then maintain a predetermined distance between the obstacleand the robotic device 100. In the first embodiment, the microprocessingunit 135 is operative, in response to signals from theobstacle-following unit, to implement small CW or CCW turns to maintainits position with respect to the obstacle. The robotic device 100implements a small CW when the robotic device 100 transitions fromobstacle detection to non-detection (reflection to non-reflection) or toimplement a small CCW turn when the robotic device 100 transitions fromnon-detection to detection (non-reflection to reflection). Similarturning behaviors are implemented by the robotic device 100 to maintainthe predetermined distance from the obstacle.

The robotic device 100 is operated in the Obstacle-Following behavioralmode for a predetermined or random period of time, for a predeterminedor random distance (e.g., a maximum or minimum distance) and/or untilthe occurrence of a specified event, e.g., activation of one or more ofthe obstacle detection units 120 a predetermined number of times(collectively a transition condition). In certain embodiments, themicroprocessor 135 will cause the robotic device to implement an Alignbehavioral mode upon activation of the obstacle-detection units 120 inthe Obstacle-Following behavioral mode wherein the implements a minimumangle CCW turn to align the robotic device 100 with the obstacle.

The Room Coverage pattern can be used by the robotic device 100 to cleanany defined working area that is bounded by walls, stairs, obstacles orother barriers (e.g., a virtual wall unit). A preferred embodiment forthe Room Coverage pattern comprises the Random-Bounce behavioral mode incombination with the Straight Line behavioral mode. Initially, therobotic device 100 travels under control of the Straight-Line behavioralmode, i.e., straight-line algorithm (main drive wheel assemblies 112L,112R operating at the same rotational speed in the same direction) untilan obstacle is encountered. Upon activation of one or more of theobstacle detection units 120, the microprocessing unit 135 is operativeto compute an acceptable range of new directions based upon the obstacledetection unit(s) 126 activated. The microprocessing unit 135 selects anew heading from within the acceptable range and implements a CW or CCWturn to achieve the new heading with minimal movement. In someembodiments, the new turn heading may be followed by forward movement toincrease the cleaning efficiency of the robotic device 100. The newheading may be randomly selected across the acceptable range ofheadings, or based upon some statistical selection scheme, e.g.,Gaussian distribution. In other embodiments of the Room Coveragebehavioral mode, the microprocessing unit 135 can be programmed tochange headings randomly or at predetermined times, without input fromthe sensor system.

The robotic device 100 is operated in the Room Coverage behavioral modefor a predetermined or random period of time, for a predetermined orrandom distance (e.g., a maximum or minimum distance) and/or until theoccurrence of a specified event, e.g., activation of theobstacle-detection units 120 a predetermined number of times(collectively a transition condition).

By way of example, the robotic device 100 can include four escapebehavioral modes: a Turn behavioral mode, an Edge behavioral mode, aWheel Drop behavioral mode, and a Slow behavioral mode. One skilled inthe art will appreciate that other behavioral modes can be utilized bythe robotic device 100. One or more of these behavioral modes may beimplemented, for example, in response to a current rise in one of theelectric motors 116, 118 of the side brush assembly 140 or dual-stagebrush assembly above a low or high stall threshold, forward bumper 106in compressed position for determined time period, detection of awheel-drop event.

In the Turn behavioral mode, the robotic device 100 turns in place in arandom direction, starting at higher velocity (e.g., twice normalturning velocity) and decreasing to a lower velocity (one-half normalturning velocity), i.e., small panic turns and large panic turns,respectively. Low panic turns are preferably in the range of 45.degree.to 90.degree., large panic turns are preferably in the range of90.degree. to 270.degree. The Turn behavioral mode prevents the roboticdevice 100 from becoming stuck on room impediments, e.g., high spot incarpet, ramped lamp base, from becoming stuck under room impediments,e.g., under a sofa, or from becoming trapped in a confined area.

In the Edge behavioral mode follows the edge of an obstacle unit it hasturned through a predetermined number of degrees, e.g., 60.degree.,without activation of any of the obstacle detection units 120, or untilthe robotic device has turned through a predetermined number of degrees,e.g., 170.degree., since initiation of the Edge behavioral mode. TheEdge behavioral mode allows the robotic device 100 to move through thesmallest possible openings to escape from confined areas.

In the wheel Drop behavioral mode, the microprocessor 135 reverses thedirection of the main wheel drive assemblies 112L, 112R momentarily,then stops them. If the activated wheel drop sensor 124 deactivateswithin a predetermined time, the microprocessor 135 then reimplementsthe behavioral mode that was being executed prior to the activation ofthe wheel drop sensor 124.

In response to certain events, e.g., activation of a wheel drop sensor124 or a cliff detector 122, the Slow behavioral mode is implemented toslowed down the robotic device 100 for a predetermined distance and thenramped back up to its normal operating speed.

When a safety condition is detected by the sensor subsystem, e.g., aseries of brush or wheel stalls that cause the corresponding electricmotors to be temporarily cycled off, wheel drop sensor 124 or a cliffdetection sensor 122 activated for greater that a predetermined periodof time, the robotic device 100 is generally cycled to an off state. Inaddition, an audible alarm may be generated.

The foregoing description of behavioral modes for the robotic device 100is merely representative of the types of operating modes that can beimplemented by the robotic device 100. One skilled in the art willappreciate that the behavioral modes described above can be implementedin other combinations and/or circumstances, and other behavioral modesand patterns of movement are also possible.

III. Debris Sensor Structure and Operation

As shown in FIGS. 1-3, in accordance with the present invention, anautonomous cleaning device (and similarly, a non-autonomous cleaningdevice as shown by way of example in FIG. 7) can be improved byincorporation of a debris sensor. In the embodiment illustrated in FIGS.1 and 3, the debris sensor subsystem comprises left and rightpiezoelectric sensing elements 125L, 125R situated proximate to orwithin a cleaning pathway of a cleaning device, and electronics forprocessing the debris signal from the sensor for forwarding to amicroprocessor 135 or other controller.

When employed in an autonomous, robot cleaning device, the debris signalfrom the debris sensor can be used to select a behavioral mode (such asentering into a spot cleaning mode), change an operational condition(such as speed, power or other), steer in the direction of debris(particularly when spaced-apart left and right debris sensors are usedto create a differential signal), or take other actions.

A debris sensor according to the present invention can also beincorporated into a non-autonomous cleaning device. When employed in anon-autonomous cleaning device such as, for example, an otherwiserelatively conventional vacuum cleaner 700 like that shown in FIG. 7,the debris signal 706 generated by a piezoelectric debris sensor 704PSsituated within a cleaning or vacuum pathway of the device can beemployed by a controlling microprocessor 708 in the body of the vacuumcleaner 702 to generate a user-perceptible signal (such as by lighting alight 710), to increase power from the power system 703, or take somecombination of actions (such as lighting a “high power” light andsimultaneously increasing power).

The algorithmic aspects of the operation of the debris sensor subsystemare summarized in FIG. 8. As shown therein, a method according to theinvention can include detecting left and right debris signalsrepresentative of debris strikes, and thus, of the presence, quantity orvolume, and direction of debris (802); selecting an operational mode orpattern of movement (such as Spot Coverage) based on the debris signalvalues (804); selecting a direction of movement based on differentialleft/right debris signals (e.g., steering toward the side with moredebris) (806); generating a user-perceptible signal representative ofthe presence of debris or other characteristic (e.g., by illuminating auser-perceptible LED) (808); or otherwise varying or controlling anoperational condition, such as power (810).

A further practice of the invention takes advantage of the motion of anautonomous cleaning device across a floor or other surface, processingthe debris signal in conjunction with knowledge of the cleaning device'smovement to calculate a debris gradient (812 in FIG. 8). The debrisgradient is representative of changes in debris strikes count as theautonomous cleaning apparatus moves along a surface. By examining thesign of the gradient (positive or negative, associated with increasingor decreasing debris), an autonomous cleaning device controller cancontinuously adjust the path or pattern of movement of the device toclean a debris field most effectively (812).

Piezoelectric Sensor:

As noted above, a piezoelectric transducer element can be used in thedebris sensor subsystem of the invention. Piezoelectric sensors provideinstantaneous response to debris strikes and are relatively immune toaccretion that would

An example of a piezoelectric transducer 125PS is shown in FIG. 4.Referring now to FIG. 4, the piezoelectric sensor element 125PS caninclude one or more 0.20 millimeter thick, 20 millimeter diameter brassdisks 402 with the piezoelectric material and electrodes bonded to thetopside (with a total thickness of 0.51 mm), mounted to an elastomer pad404, a plastic dirt sensor cap 406, a debris sensor PC board withassociated electronics 408, grounded metal shield 410, and retained bymounting screws (or bolts or the like) 412 and elastomer grommets 414.The elastomer grommets provide a degree of vibration dampening orisolation between the piezoelectric sensor element 125PS and thecleaning device.

In the example shown in FIG. 4, a rigid piezoelectric disk, of the typetypically used as inexpensive sounders, can be used. However, flexiblepiezoelectric film can also be advantageously employed. Since the filmcan be produced in arbitrary shapes, its use affords the possibility ofsensitivity to debris across the entire cleaning width of the cleaningdevice, rather than sensitivity in selected areas where, for example,the disks may be located. Conversely, however, film is at presentsubstantially more expensive and is subject to degradation over time. Incontrast, brass disks have proven to be extremely robust.

The exemplary mounting configuration shown in FIG. 4 is substantiallyoptimized for use within a platform that is mechanically quite noisy,such as an autonomous vacuum cleaner like that shown in FIG. 3. In sucha device, vibration dampening or isolation of the sensor is extremelyuseful. However, in an application involving a non-autonomous cleaningdevice such as a canister-type vacuum cleaner like that shown in FIG. 7,the dampening aspects of the mounting system of FIG. 4 may not benecessary. In a non-autonomous cleaning apparatus, an alternativemounting system may involve heat staking the piezoelectric elementdirectly to its housing. In either case, a key consideration forachieving enhanced performance is the reduction of the surface arearequired to clamp, bolt, or otherwise maintain the piezoelectric elementin place. The smaller the footprint of this clamped “dead zone”, themore sensitive the piezoelectric element will be.

In operation, debris thrown up by the cleaning brush assembly (e.g.,brush 94 of FIG. 3), or otherwise flowing through a cleaning pathwaywithin the cleaning device (e.g., vacuum compartment 104 of FIG. 3) canstrike the bottom, all-brass side of the sensor 125PS (see FIG. 3). Inan autonomous cleaning device, as shown in FIG. 3, the debris sensor125PS can be located substantially at an axis AX along which main brush94 and flapper brush 92 meet, so that the particles 127 are thrown upand strike the sensor 125PS with maximum force.

As is well known, a piezoelectric sensor converts mechanical energy(e.g., the kinetic energy of a debris strike and vibration of the brassdisk) into electrical energy—in this case, generating an electricalpulse each time it is struck by debris—and it is this electrical pulsethat can be processed and transmitted to a system controller (e.g.,controller 135 of FIGS. 1 and 2 or 708 of FIG. 8) to control or cause achange in operational mode, in accordance with the invention.Piezoelectric elements are typically designed for use as audiotransducers, for example, to generate beep tones. When an AC voltage isapplied, they vibrate mechanically in step with the AC waveform, andgenerate an audible output. Conversely, if they are mechanicallyvibrated, they produce an AC voltage output. This is the manner in whichthey are employed in the present invention. In particular, when anobject first strikes the brass face of the sensor, it causes the disk toflex inward, which produces a voltage pulse.

Filtering:

However, since the sensor element 125PS is in direct or indirect contactwith the cleaning device chassis or body through its mounting system(see FIGS. 3 and 4), it is subject to the mechanical vibrations normallyproduced by motors, brushes, fans and other moving parts when thecleaning device is functioning. This mechanical vibration can cause thesensor to output an undesirable noise signal that can be larger inamplitude than the signal created by small, low mass debris (such ascrushed black pepper) striking the sensor. The end result is that thesensor would output a composite signal composed of lower frequency noisecomponents (up to approximately 16 kHz) and higher frequency, possiblylower amplitude, debris-strike components (greater than 30 kHz, up tohundreds of kHz). Thus, it is useful to provide a way to filter outextraneous signals.

Accordingly, as described below, an electronic filter is used to greatlyattenuate the lower frequency signal components to improvesignal-to-noise performance. Examples of the architecture and circuitryof such filtering and signal processing elements will next be describedin connection with FIGS. 5 and 6.

IV. Signal Processing

FIG. 5 is a schematic diagram of the signal processing elements of adebris sensor subsystem in one practice of the invention.

As noted above, one purpose of a debris sensor is to enable anautonomous cleaning apparatus to sense when it is picking up debris orotherwise encountering a debris field. This information can be used asan input to effect a change in the cleaning behavior or cause theapparatus to enter a selected operational or behavioral mode, such as,for example, the spot cleaning mode described above when debris isencountered. In an non-autonomous cleaning apparatus like that shown inFIG. 7, the debris signal 706 from the debris sensor 704PS can be usedto cause a user-perceptible light 710 to be illuminated (e.g., to signalto the user that debris is being encountered), to raise power outputfrom the power until 703 to the cleaning systems, or to cause some otheroperational change or combination of changes (e.g., lighting auser-perceptible “high power” light and simultaneously raising power).

Moreover, as noted above, two debris sensor circuit modules (i.e., leftand right channels like 125L and 125R of FIG. 1) can be used to enablean autonomous cleaning device to sense the difference between theamounts of debris picked up on the right and left sides of the cleaninghead assembly. For example, if the robot encounters a field of dirt offto its left side, the left side debris sensor may indicate debris hits,while the right side sensor indicates no (or a low rate of debris hits.This differential output could be used by the microprocessor controllerof an autonomous cleaning device (such as controller 135 of FIGS. 1 and2) to steer the device in the direction of the debris (e.g., to steerleft if the left-side debris sensor is generating higher signal valuesthan the right-side debris sensor); to otherwise choose a vector in thedirection of the debris; or to otherwise select a pattern of movement orbehavior pattern such as spot coverage or other.

Thus, FIG. 5 illustrates one channel (for example, the left-sidechannel) of a debris sensor subsystem that can contain both left andright side channels. The right side channel is substantially identical,and its structure and operation will therefore be understood from thefollowing discussion.

As shown in FIG. 5, the left channel consists of a sensor element(piezoelectric disk) 402, an acoustic vibration filter/RFI filter module502, a signal amplifier 504, a reference level generator 506, anattenuator 508, a comparator 510 for comparing the outputs of theattenuator and reference level generator, and a pulse stretcher 512. Theoutput of the pulse stretcher is a logic level output signal to a systemcontroller like the processor 135 shown in FIG. 2; i.e., a controllersuitable for use in selecting an operational behavior.

The Acoustic Vibration Filter/RFI Filter block 502 can be designed toprovide significant attenuation (in one embodiment, better than −45 dBVolts), and to block most of the lower frequency, slow rate of changemechanical vibration signals, while permitting higher frequency, fastrate of change debris-strike signals to pass. However, even though thesehigher frequency signals get through the filter, they are attenuated,and thus require amplification by the Signal Amplifier block 504.

In addition to amplifying the desired higher frequency debris strikesignals, the very small residual mechanical noise signals that do passthrough the filter also get amplified, along with electrical noisegenerated by the amplifier itself, and any radio frequency interference(RFI) components generated by the motors and radiated through the air,or picked up by the sensor and its conducting wires. The signalamplifier's high frequency response is designed to minimize theamplification of very high frequency RFI. This constant background noisesignal, which has much lower frequency components than the desireddebris strike signals, is fed into the Reference Level Generator block506. The purpose of module 506 is to create a reference signal thatfollows the instantaneous peak value, or envelope, of the noise signal.It can be seen in FIG. 5 that the signal of interest, i.e., the signalthat results when debris strikes the sensor, is also fed into thisblock. Thus, the Reference Level Generator block circuitry is designedso that it does not respond quickly enough to high frequency, fast rateof change debris-strike signals to be able to track the instantaneouspeak value of these signals. The resulting reference signal will be usedto make a comparison as described below.

Referring again to FIG. 5, it will be seen that the signal fromamplifier 504 is also fed into the Attenuator block. This is the samesignal that goes to the Reference Level Generator 506, so it is acomposite signal containing both the high frequency signal of interest(i.e., when debris strikes the sensor) and the lower frequency noise.The Attenuator 508 reduces the amplitude of this signal so that itnormally is below the amplitude of the signal from the Reference LevelGenerator 506 when no debris is striking the sensor element.

The Comparator 510 compares the instantaneous voltage amplitude value ofthe signal from the Attenuator 508 to the signal from the ReferenceLevel Generator 506. Normally, when the cleaning device operating isrunning and debris are not striking the sensor element, theinstantaneous voltage coming out of the Reference Level Generator 506will be higher than the voltage coming out of the Attenuator block 508.This causes the Comparator block 510 to output a high logic level signal(logic one), which is then inverted by the Pulse Stretcher block 512 tocreate a low logic level (logic zero).

However, when debris strikes the sensor, the voltage from the Attenuator508 exceeds the voltage from the Reference Level Generator 506 (sincethis circuit cannot track the high frequency, fast rate of change signalcomponent from the Amplifier 504) and the signal produced by a debrisstrike is higher in voltage amplitude than the constant backgroundmechanical noise signal which is more severely attenuated by theAcoustic Vibration Filter 502. This causes the comparator to momentarilychange state to a logic level zero. The Pulse Stretcher block 512extends this very brief (typically under 10-microsecond) event to aconstant 1 millisecond (+0.3 mS, −0 mS) event, so as to provide thesystem controller (e.g., controller 135 of FIG. 2) sufficient time tosample the signal.

When the system controller “sees” this 1-millisecond logic zero pulse,it interprets the event as a debris strike.

Referring now to the RFI Filter portion of the Acoustic VibrationFilter/RFI Filter block 502, this filter serves to attenuate the veryhigh frequency radiated electrical noise (RFD), which is generated bythe motors and motor driver circuits.

In summary, the illustrated circuitry connected to the sensor elementuses both amplitude and frequency information to discriminate a debrisstrike (representative of the cleaning device picking up debris) fromthe normal background mechanical noise also picked up by the sensorelement and the radiated radio frequency electrical noise produced bythe motors and motor driver circuits. The normal, though undesirable,constant background noise is used to establish a dynamic reference thatprevents false debris-strike indications while maintaining a goodsignal-to-noise ratio.

In practice, the mechanical mounting system for the sensor element (seeFIG. 4) is also designed to help minimize the mechanical acoustic noisevibration coupling that affects the sensor element.

Signal Processing Circuitry:

FIG. 6 is a detailed schematic diagram of exemplary debris sensorcircuitry. Those skilled in the art will understand that in otherembodiments, the signal processing can be partially or entirelycontained and executed within the software of the microcontroller 135.With reference to FIG. 6, the illustrated example of suitable signalprocessing circuitry contains the following elements, operating inaccordance with the following description:

The ground referenced, composite signal from the piezoelectric sensordisk (see piezoelectric disk 402 of FIG. 4) is fed into the capacitorC1, which is the input to the 5-pole, high pass, passive R-C filterdesigned to attenuate the low frequency, acoustic mechanical vibrationsconducted into the sensor through the mounting system. This filter has a21.5 kHz, −3 dB corner frequency rolling off at −100 dB/Decade. Theoutput of this filter is fed to a signal pole, low pass, passive R-Cfilter designed to attenuate any very high frequency RFI. This filterhas a 1.06 MHz, 31 3 dB corner frequency rolling off at −20 dB/Decade.The output of this filter is diode clamped by D1 and D2 in order toprotect U1 from high voltage transients in the event the sensor elementsustains a severe strike that generates a voltage pulse greater than theamplifier's supply rails. The DC biasing required for signal-supplyoperation for the amplifier chain and subsequent comparator circuitry iscreated by R5 and R6. These two resistor values are selected such thattheir thevenin impedance works with C5 to maintain the filter's fifthpole frequency response correctly.

U1A, U1B and their associated components form a two stage, ac-coupled,non-inverting amplifier with a theoretical AC gain of 441. C9 and C10serve to minimize gain at low frequencies while C7 and C8 work to rollthe gain off at RFI frequencies. The net theoretical frequency responsefrom the filter input to the amplifier output is a single pole high passresponse with −3 dB at 32.5 kHz, −100 dB/Decade, and a 2-pole low passresponse with break frequencies at 100 kHz, −32 dB/Decade, and 5.4 MHz,−100 dB/Decade, together forming a band-pass filter.

The output from the amplifier is split, with one output going into R14,and the other to the non-inverting input of U1C. The signal going intoR14 is attenuated by the R14-R15 voltage divider, and then fed into theinverting input of comparator U2A. The other signal branch from theoutput of U1B is fed into the non-inverting input of amplifier U1C. UICalong with U1D and the components therebetween (as shown in FIG. 2) forma half-wave, positive peak detector. The attack and decay times are setby R13 and R12, respectively. The output from this circuit is fed to thenon-inverting input of U2A through R16. R16 along with R19 providehysteresis to improve switching time and noise immunity. U2A functionsto compare the instantaneous value between the output of the peakdetector to the output of the R14-R15 attenuator.

Normally, when debris is not striking the sensor, the output of the peakdetector will be greater in amplitude than the output of the attenuatornetwork. When debris strikes the sensor, a high frequency pulse iscreated that has a higher amplitude coming out of the front-end highpass filter going into U1A than the lower frequency mechanical noisesignal component. This signal will be larger in amplitude, even aftercoming out of the R14-R15 attenuator network, than the signal coming outof the peak detector, because the peak detector cannot track high-speedpulses due to the component values in the R13, C11, R12 network. Thecomparator then changes state from high to low for as long as theamplitude of the debris-strike pulse stays above the dynamic, noisegenerated, reference-level signal coming out of the peak detector. Sincethis comparator output pulse can be too short for the system controllerto see, a pulse stretcher is used.

The pulse stretcher is a one-shot monostable design with a lockoutmechanism to prevent re-triggering until the end of the timeout period.The output from U2A is fed into the junction of C13 and Q1. C13 couplesthe signal into the monostable formed by U2C and its associatedcomponents. Q1 functions as the lockout by holding the output of U2A lowuntil the monostable times out. The timeout period is set by the timeconstant formed by R22, C12 and R18, and the reference level set by theR20-R21 voltage divider. This time can adjusted for 1 mS, +0.3 mS, −0.00mS as dictated by the requirements of the software used by thecontroller/processor.

Power for the debris sensor circuit is provided by U3 and associatedcomponents. U3 is a low power linear regulator that provides a 5-voltoutput. The unregulated voltage from the robot's onboard batteryprovides the power input.

When required, circuit adjustments can be set by R14 and R12. Theseadjustments will allow the circuit response to be tuned in a shortperiod of time In a production device of this kind, it is expected thatpower into, and signal out of the debris sensor circuit printed circuitboard (PCB) will be transferred to the main board via shielded cable.Alternatively, noise filters may be substituted for the use of shieldedcable, reducing the cost of wiring. The cable shield drain wire can begrounded at the sensor circuit PCB side only. The shield is not to carryany ground current. A separate conductor inside the cable will carrypower ground. To reduce noise, the production sensor PCB should have allcomponents on the topside with solid ground plane on the bottom side.The sensor PCB should be housed in a mounting assembly that has agrounded metal shield that covers the topside of the board to shield thecomponents from radiated noise pick up from the robot's motors. Thepiezoelectric sensor disk can be mounted under the sensor circuit PCB ona suitable mechanical mounting system, such as that shown in FIG. 4, inorder to keep the connecting leads as short as possible for noiseimmunity.

V. Conclusions

The invention provides a debris sensor that is not subject todegradation by accretion of debris, but is capable of instantaneouslysensing and responding to debris strikes, and thus immediatelyresponsive to debris on a floor or other surface to be cleaned, withreduced sensitivity to variations in airflow, instantaneous power, orother operational conditions of the cleaning device.

When employed as described herein, the invention enables an autonomouscleaning device to control its operation or select from amongoperational modes, patterns of movement or behaviors responsive todetected debris, for example, by steering the device toward “dirtier”areas based on signals generated by the debris sensor.

The debris sensor can also be employed in non-autonomous cleaningdevices to control, select or vary operational modes of either anautonomous or non-autonomous cleaning apparatus.

In addition, the disclosed signal processing architecture and circuitryis particularly useful in conjunction with a piezoelectric debris sensorto provide high signal to noise ratios.

Those skilled in the art will appreciate that a wide range ofmodifications and variations of the present invention are possible andwithin the scope of the invention. The debris sensor can also beemployed for purposes, and in devices, other than those describedherein. Accordingly, the foregoing is presented solely by way ofexample, and the scope of the invention is limited solely by theappended claims.

We claim:
 1. An autonomous cleaning apparatus comprising: a chassis; adrive system disposed on the chassis and configured to move of thecleaning apparatus over a cleaning surface; a receptacle disposed on thechassis; a cleaning head system disposed on the chassis and configuredto move debris from the cleaning surface toward the receptacle; a firstand a second debris impact sensing element, each debris impact sensingelement carried by the chassis and arranged to detect the debris movedtoward the dust bin wherein each of the first and second debris sensingelements is configured to generate an electrical pulse in response tobeing struck with debris; a controller in communication with the drivesystem and the first and second debris impact sensing elements, thecontroller configured to steer the drive system immediately in a patternof movement based at least in part on a signal received from at leastone of the first and second debris impact sensing elements.
 2. Theautonomous cleaning apparatus of claim 1 wherein the chassis has a rightside and a left side and the first debris sensing element is disposed onthe right side of the chassis and the second debris sensing element isdisposed on the left side of the chassis.
 3. The autonomous cleaningapparatus of claim 2 wherein the controller is further configured tosteer the drive system in the direction of the signal received from atleast one of the first and second debris sensing elements.
 4. Theautonomous cleaning apparatus of claim 1 wherein the cleaning headsystem defines a cleaning width and at least one of the first and seconddebris sensing elements is sensitive to debris across the entirecleaning width.
 5. The autonomous cleaning apparatus of claim 1 furthercomprising an electronic filter in electrical communication with thefirst debris sensing element, the electronic filter configured toattenuate at least a portion of the signal received from the firstdebris sensing element.
 6. The autonomous cleaning apparatus of claim 1wherein the first debris sensing element is spaced apart from the seconddebris sensing element and the controller is further configured todetermine a debris gradient based at least in part on respective signalsreceived from the first and second debris sensing elements.
 7. Theautonomous cleaning apparatus of claim 6 wherein the controller isfurther configured to steer the drive system in the direction of debrisbased at least in part on the determined debris gradient.
 8. Theautonomous cleaning apparatus of claim 6 wherein the controller isfurther configured to adjust continuously the movement of the drivesystem based at least in part on the determined debris gradient.
 9. Theautonomous cleaning apparatus of claim 1 wherein the controller isfurther configured to select a pattern of movement of the drive systembased at least in part on the signal received from the at least one ofthe first and second debris sensing elements.
 10. The autonomouscleaning apparatus of claim 9 wherein the pattern of movement of thedrive system comprises a spot coverage mode.
 11. The autonomous cleaningapparatus of claim 10 wherein the spot coverage mode comprises movementof the drive system in a self-bounded area.
 12. The autonomous cleaningapparatus of claim 1 wherein the receptacle is a removable dustcartridge and the cleaning head system comprises a brush arranged todirect debris to the removable dust cartridge.
 13. The autonomouscleaning apparatus of claim 1 further comprising a user-perceptiblesignal in communication with the first and second debris sensingelements, wherein the user-perceptible signal is configured to alert auser to debris encountered by at least one of the first and seconddebris sensing elements.
 14. The autonomous cleaning apparatus of claim1 wherein each of the first and second debris sensing elements isconfigured to convert kinetic energy of a debris strike into electricalenergy.
 15. The autonomous cleaning apparatus of claim 14 wherein eachof the first and second debris sensing elements comprises apiezoelectric transducer.
 16. A method of controlling an autonomouscleaning apparatus, the method comprising: moving the autonomouscleaning apparatus over a cleaning surface; receiving a signal from atleast one of a first and a second debris impact sensing element carriedon the autonomous cleaning apparatus, the signal representative of theimpact of debris on a cleaning surface, wherein each of the first andsecond debris sensing elements is configured to generate an electricalpulse in response to being struck with debris; and steering theautonomous cleaning apparatus immediately in a pattern of movement basedat least in part on the received signal.
 17. The method of claim 16further comprising determining a debris gradient based at least in parton the received signal from at least one of the first and second debrissensing elements, wherein steering the autonomous cleaning apparatusimmediately in a pattern of movement comprises steering the autonomouscleaning apparatus in the direction of the determined debris gradient.18. The method of claim 17 further comprising continuously adjustingmovement of the autonomous cleaning apparatus based at least in part onthe determined debris gradient.
 19. The method of claim 16 furthercomprising selecting a pattern of movement of the autonomous cleaningapparatus based at least in part on the received signal.
 20. The methodof claim 19 wherein selecting a pattern of movement of the autonomouscleaning apparatus comprises selecting a spot coverage mode.